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Corrections BIOPHYSICS AND COMPUTATIONAL BIOLOGY Correction for “Assessing the utility of coevolution-based residue– The authors note that Fig. 1 C and E and the corresponding residue contact predictions in a sequence- and structure-rich era,” legend appeared incorrectly. The corrected figure and its legend by Hetunandan Kamisetty, Sergey Ovchinnikov, and David Baker, appear below. which appeared in issue 39, September 24, 2013, of Proc Natl Acad Sci USA (110:15674–15679; first published September 5, 2013; 10.1073/pnas.1314045110). ABCD 1 1 1 1 0.8 0.8 0.8 0.8 0.6 0.6 0.6 0.6 0.4 0.4 0.4 0.4 GREMLIN 0.2 0.2 0.2 0.2 GREMLIN(no prior) GREMLIN(no prior) GREMLIN(no prior) 0.2 0.4 0.6 0.8 1 0.2 0.4 0.6 0.8 1 0.2 0.4 0.6 0.8 1 0.2 0.4 0.6 0.8 1 DCA PSICOV MIc GREMLIN(no prior) EFG1 1 0.8 0.8 0.8 GREMLIN 0.6 0.6 0.6 GREMLIN (no prior) PSICOV DCA 0.4 0.4 MIc 0.4 Accuracy Accuracy at L/2 0.2 Accuracy at L/5 0.2 0.2 Fraction of Targets L/2 L 3L/2 1 5 10 20 1 5 10 20 Number of Predictions Sequences Per Position Sequences Per Position Fig. 1. Accuracy of contact prediction. Comparison of GREMLIN with DCA (A), PSICOV (B), MIc (C), and GREMLIN when prior information is used (D). Each point corresponds to a protein, the axes indicate the accuracy of the top ranked L/2 Cβ−Cβ contacts predicted by the indicated methods. (E) (solid lines) Average accuracy for varying numbers of predictions; (broken lines) fraction of targets where GREMLIN was more accurate than the indicated method. Dependence of accuracy of the top L/5 (F) and L/2 (G) predictions on the alignment depth for a subset of 75 targets with deep alignments. www.pnas.org/cgi/doi/10.1073/pnas.1319550110 18734–18735 | PNAS | November 12, 2013 | vol. 110 | no. 46 www.pnas.org Downloaded by guest on September 27, 2021 NEUROSCIENCE Correction for “Trafficking of gap junction channels at a verte- Sci USA (109:E573–E582; first published February 7, 2012; brate electrical synapse in vivo,” by Carmen E. Flores, Srikant 10.1073/pnas.1121557109). Nannapaneni, Kimberly G. V. Davidson, Thomas Yasumura, The authors note that the legend for Fig. 4 appeared incorrectly. Michael V. L. Bennett, John E. Rash, and Alberto E. Pereda, The figure and its corrected legend appear below. which appeared in issue 9, February 28, 2012, of Proc Natl Acad Fig. 4. Presence of endocytic and exocytic machinery in CEs. CEs are identified by immunofluorescence connexin labeling with monoclonal anti-Cx35/36 (mCx35) (green). (A) Diagram of the M-cell. (Inset) Confocal projection of a single CE (from Fig. 4D of ref. 23; this false-color image was rotated and recolored for consistency with adjacent immunofluorescence). Single-terminal images in this figure represent the average of three to five z-sections; the dotted line denotes the perimeter of a single CE. (B) Confocal projection of a portion of the lateral dendrite of the M-cell using double immunolabeling with polyclonal anti-Cx36 (pCx36; Zymed 36-4600; green) and monoclonal anti-SNAP-25 (mSNAP-25; red) antibodies. (C and D) Confocal projection of single CEs using double immunolabeling with anti-Cx36 (green) and monoclonal anti–SNAP-25 (red) antibodies. In en face view (C), SNAP-25 was not restricted to the periphery of the terminals, where glutamate receptors and active zones are concentrated, but also was found in the central region where GJs predominate (arrowheads).(E and F) As with SNAP-25, some dynamin labeling (monoclonal antibody) was closely associated with labeling with anti-Cx36 (arrowheads), consistent with endocytosis of cell–cell channels. The image in F is a tilted side view of a CE, whose contact area is characteristically concave with the center protruding into the M-cell. The red dotted line in F indicates the approximate position of the cell surface (“M-cell” indicates the dendritic side). The approach does not distinguish between presynaptic and postsynaptic locations of connexin labeling. Both dynamin and SNAP-25 labeling also were observed in the vicinity of CEs (asterisks in D and E). Most of these sites were anti-Cx36 negative and likely correspond to small inhibitory boutons (65). www.pnas.org/cgi/doi/10.1073/pnas.1319624110 CORRECTIONS PNAS | November 12, 2013 | vol. 110 | no. 46 | 18735 Downloaded by guest on September 27, 2021 Trafficking of gap junction channels at a vertebrate PNAS PLUS electrical synapse in vivo Carmen E. Floresa, Srikant Nannapanenia, Kimberly G. V. Davidsonb, Thomas Yasumurab, Michael V. L. Bennetta,1, John E. Rashb,c, and Alberto E. Peredaa,1 aDominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461; bDepartment of Biomedical Sciences, Colorado State University, Fort Collins, CO 80523; and cProgram in Cell and Molecular Biology, Colorado State University, Fort Collins, CO 80523 Contributed by Michael V. L. Bennett, December 30, 2011 (sent for review December 22, 2011) Trafficking and turnover of transmitter receptors required to main- connexons are removed from the center of the plaques (15–18) as tain and modify the strength of chemical synapses have been char- intact regions of the junction that are internalized into one or the acterized extensively. In contrast, little is known regarding trafficking other of the coupled cells, with larger internalized areas forming of gap junction components at electrical synapses. By combining double-membrane vesicles that in thin sections can appear as an- ultrastructural and in vivo physiological analysis at identified mixed nular GJs (asterisk in Fig. 1B). These structures subsequently are (electrical and chemical) synapses on the goldfish Mauthner cell, we transported to lysosomes, where they are degraded (17, 19). show here that gap junction hemichannels are added at the edges of However, whether these processes occur in native neuronal GJs in GJ plaques where they dock with hemichannels in the apposed vivo remains unknown. membrane to form cell–cell channels and, simultaneously, that intact We investigated trafficking of GJ channels and the functional junctional regions are removed from centers of these plaques into relevance of this trafficking at identifiable mixed (electrical and either presynaptic axon or postsynaptic dendrite. Moreover, electri- chemical) synapses on the goldfish Mauthner (M-) cell. These cal coupling is readily modified by intradendritic application of pep- synapses are the large myelinated club endings or simply club tides that interfere with endocytosis or exocytosis, suggesting that endings (CEs) (Fig. 1A) (20). CEs are advantageous for correla- the strength of electrical synapses at these terminals is sustained, at tions of their structural and biochemical features with their in vivo least in part, by fast (in minutes) turnover of gap junction channels. A physiological properties and provide a valuable model for the study peptide corresponding to a region of the carboxy terminus that is of vertebrate electrical transmission (21, 22). CEs are unusually NEUROSCIENCE conserved in Cx36 and its two teleost homologs appears to interfere large (5–10 μm in diameter), and each has ∼100 GJ plaques and up with formation of new gap junction channels, presumably by reduc- to ∼100,000 channels, containing connexin 35 (Cx35) (23), a fish ing insertion of hemichannels on the dendritic side. Thus, our data ortholog of the mammalian neuronal connexin, Cx36 (24). Recent indicate that electrical synapses are dynamic structures and that their data indicate that a second homolog of Cx36, Cx34.7, also is channels are turned over actively, suggesting that regulated traffick- present at these terminals (25). Both electrical and chemical ing of connexons may contribute to the modification of gap junc- components of transmission can undergo long-term potentiation tional conductance. or depression as a result of presynaptic impulse activity (26–30). Consistent with these dynamic properties, we found ultrastructural connexin | synaptic plasticity | auditory | potentiation | freeze-fracture evidence for active insertion of hemichannels and removal of cell– cell channels at these GJs that may contribute to the dynamic onstitutive and regulated trafficking of ion channels to and properties. We found that electrical transmission was strengthened Cfrom the plasma membrane are important processes for the in minutes by intradendritic application of peptides that interfere maintenance of cell function and responsiveness to environmental with endocytosis and weakened by peptides that reduce insertion stimuli. Trafficking of ionotropic receptors involving processes of of new hemichannels, indicating fast turnover of GJ channels. insertion and retrieval maintains the strength of chemical synapses Furthermore, intradendritic application of a peptide correspond- and underlies several forms of synaptic plasticity (1–4). Trafficking ing to the last 15 amino acids of the CT of Cx36, including a PDZ- usually requires interactions between the receptor’s carboxy ter- binding domain (31) (a region that is highly conserved between fi minus (CT) and a variety of cytosolic proteins, including those Cx36 and its sh homologs), progressively depressed electrical forming scaffolds (3, 5–9). In contrast, little is known regarding the transmission, suggesting that this portion of the molecule con- involvement of channel trafficking in modulating the strength of tributes to targeting and/or insertion of new GJ hemichannels. gap junction (GJ)-mediated electrical transmission. Taken together, our data indicate the existence of active turnover Vertebrate GJs are clusters (plaques) of aqueous integral of GJ channels in vivo; this turnover may be modulated to increase membrane protein channels that connect the interiors of the or decrease synaptic strength. coupled cells. Each channel is formed by the docking of two hex- Results americ connexin hemichannels, or connexons, one contributed by Ultrastructural Evidence for Trafficking of GJ Channels.